On Tue, 8 Dec 2009, Alan Stern wrote: > > That's not the way it should be done. Linus had children taking their > parents' locks during suspend, which is simple but leads to > difficulties. No it doesn't. Name them. > Instead, the PM core should do a down_write() on each device before > starting the device's async suspend routine, and an up_write() when the > routine finishes. No you should NOT do that. If you do that, you serialize the suspend incorrectly and much too early. IOW, think a topology like this: a -> b -> c \ > d -> e where you'd want to suspend 'c' and 'e' asynchronously. If we do a 'down-write()' on b, then we'll delay until 'c' has suspended, an if we have ordered the nodes in the obvious depth-first order, we'll walk the PM device list in the order: c b e d a and now we'll serialize on 'b', waiting for 'c' to suspend. Which we do _not_ want to do, because the whole point was to suspend 'c' and 'e' together. > Parents should, at the start of their async routine, > do down_read() on each of their children plus whatever other devices > they need to wait for. The core can do the waiting for children part > and the driver's suspend routine can handle any other waiting. Why? That just complicates things. Compare to my simple locking scheme I've quoted several times. Linus -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
